As is known, the treatment of congestive heart failure by a CHF apparatus consists of removing patient fluid overload by means of pure ultrafiltration. Fluid removal therapy is commonly referred to as SCUF (Slow Continuous Ultra-Filtration) and is basically performed by means of an extracorporeal blood circuit including a hemofilter, an anticoagulation means (syringe pump), a fluid removal device (e.g. roller pump) and safety devices (air and blood leak detectors, pressure sensors, patient sensor).
Moreover it is known to perform extracorporeal blood treatments (such as hemodialysis, hemodiafiltration, hemoperfusion, etc.) by means of blood circuits of the single needle type, in which blood is withdrawn from, and returned to, the patient's circulatory system through a single needle with a Y-shaped junction. In these circuits, blood may be alternately cycled from and to the patient's body by a single blood pump, or by arterial and venous blood pumps, respectively. During a first (withdrawal or arterial) phase of operation, blood is drawn from the patient and pumped into the treatment device (exchanger of a semipermeable membrane type) by the arterial blood pump. Blood is prevented from returning to the needle by the closure of a valve (clamp) located between the outlet of the arterial pump and the needle, or through a clamping action of the venous blood pump. Blood pressure within the blood circuit builds until a time at which the arterial pump is turned off, the valve is opened, or the venous pump in a two-pump system is turned on to pump the blood out of the treatment device and back to the patient during a second (return or venous) phase of operation. After the return of a desired amount of blood to the patient, the venous phase is terminated and the cycle repeats. The single needle system has the advantage of half the number of needle insertions, which may be psychologically attractive to the patient, as well as prolonging the life of the fistula into which the needle is normally inserted.
U.S. Pat. No. 4,231,366 discloses a single needle system used in connection with such treatments as blood dialysis, blood perfusion and blood diafiltration, in which an arterial blood pump operates during the blood withdrawal phase as well as during the blood return phase, whereas a venous blood pump only operates during the blood return phase with a pumping rate which is larger than the rate of the arterial pump. The return blood flow pumped by the venous pump is divided in the junction member so that a proportion is returned to the patient through the needle and another proportion is pumped again by the arterial pump in accordance with the pumping rate of the arterial pump, whereby the blood is subjected repeatedly to a cleaning operation in the treatment device.